The present invention relates, in general, to integrated circuits and, more particularly, to integrated circuits having phase detectors.
In electronic systems such as cellular or wireless telephones, and synchronous demodulators, among others, a phase and frequency relationship exists between an incoming reference signal or a lower frequency translated signal and a signal generated by a voltage Controlled Oscillator (VCO). Typically, an analog phase detector locks the VCO generated signal to the incoming reference signal such that the two signals are ninety degrees out of phase with respect to each other, i.e., the two signals are phase-locked in quadrature.
The incoming reference signal can be a modulated signal containing information that is recovered in a receiver of the electronic system. The modulated signal and the signal generated by the Local Oscillator (LO) can be mixed to translate the frequency of the modulated signal from a Radio Frequency (RF) range to a signal in a lower Intermediate Frequency (IF) range before being demodulated. Additionally, in an image rejection receiver the reference signal can be mixed with a phase shifted signal from the VCO to generate a second translated signal in the IF range. An additional ninety degree phase shift in the second signal causes the second IF signal to be in-phase with the first IF signal. Translating the modulated signal to generate first and second signals that are in phase with each other allows the information in the modulated signal to be recovered and the image signals to be canceled.
However, the combined phase shifting of the two phase shifters used in generating the second signal should equal one hundred and eighty degrees as one of the conditions for image cancellation. Any inaccuracies in phase shifting generate an undesired quadrature component during translation of the modulated signal. Thus, accurate phase shifting is necessary for preventing an undesired quadrature distortion in the modulated signal information and an increase in the undesired image signal.
Accordingly, it would be advantageous to have a method and receiver circuit for locking the reference signal in-phase with the VCO generated signal. It would be of further advantage for the receiver circuit to be capable of operating at high frequencies.